144 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
and thereby make it more susceptible of infiltration, it would be well to 
thoroughly soak the seeds in water before hardening in alcohol. This 
was tried, and there was a great improvement in the results. Fewer of 
the sections went to pieces after they were transferred to the slide, and 
the parts of the seed kept their respective positions much better. 
In order to study the microscopic structure of seeds, much more 
satisfactory results can be obtained if the sections are kept in series. 
It is often necessary to have two or more successive sections before a 
correct idea of the seed can be obtained. 
The method is a modification of the one used and taught in the 
histological laboratories of Cornell University. In its practical appli- 
cation it is as follows : — In choosing seeds to section, great care is taken 
to get those which are well filled. This precaution is especially im- 
portant, as many seeds, for various reasons, never develope more than 
the coats or the enveloping ovary coats. If a seed has a straight embryo, 
or even a bent or curved one, it is better to determine by dissection just 
how the parts of the embryo are arranged with reference to the external 
parts of the seed. Thus, the seeds of Helianthus tuberosus are flat- 
tened, and slightly wedge-shaped. The embryo within is straight, and 
the upper or inner surface of the cotyledons lie in a plane parallel to 
the plane in which the seed is flattened. Moreover, the cotyledons are 
in the upper broader end of the seed. Where the seed has no external 
character, as in a Eupatorium , by which the position of its internal 
parts may be located, one has either to take the chances of getting the 
sections in the right plane, or open the coats enough to see how the parts 
are arranged, and then mark the seed in some way. Having selected a 
well-filled seed, I next put them in water at the ordinary temperature 
of the laboratory from 24 to 36 hours. From the water they are trans- 
ferred to weak alcohol (40 per cent.), and gradually hardened by trans- 
ferring to stronger until they are in 95 per cent, alcohol. Schultze’s 
apparatus may be used to advantage in hardening. Next transfer to 
equal parts of alcohol and chloroform for from 4 to 8 hours, the time 
depending on the size of the seeds. Then in pure chloroform for the 
same length of time. Then for 24 hours into chloroform with as much 
paraffin in it as it will dissolve at the ordinary temperature. From this 
into paraffin softened with chloroform, the melting-point of which is 
about 36° 0. The specimens are kept in this melted paraffin 24 hours. 
I have always been careful not to let the temperature go above 47° C., 
although I think it probable that a somewhat higher temperature would 
not injure the tissue of a seed. From this the seed may be imbedded in 
hard paraffin, and will be found to be thoroughly infiltrated. 
The seeds may be sectioned in the paraffin blocks either free-hand 
or with a microtome. It is highly essential that the sections be 
kept in series, and that none be missing. The texture of a seed is so 
fragile that when cut in thin sections the least carelessness may spoil 
a section. A very effectual way to keep sections intact when they are 
cut in paraffin is that proposed by Dr. Mark.* It consists in collo- 
dionizing the object as the sections are taken. Very thin collodion 
should be used, and applied to the cut surface after the section is taken, 
Lee t recommends that ‘ the collodion be of such a consistency that, 
* Amer. Nat., 1885, p. G28. f ‘Vade-mecum,’ 2nd ed., p. 150. 
